The overall goal of this proposal is to examine the role that the cardiac extracellular matrix (ECM) plays in the growth and remodeling of ventricular myocardium, both by its contribution to the mechanics of the ventricular wall and by mediating mechanotransduction via cell-matrix interactions. In preliminary studies, ECM mutations in vivo led to significant perturbations of ventricular development in the osteogenesis imperfecta murine (oim) and significantly impaired post-infarction remodeling in the decorin-null (DKO) mouse. In vitro studies implicate integrins as stretch transducers in isolated cardiac cells. There are three specific aims: (1) to investigate how deficiency of type I collagen in the ECM alters myocardial mechanics and leads to developmental adaptations in myocardial structure, time courses of left ventricular (LV) residual strain, myofiber geometry, and orientation will be measured in relation to the postnatal development of collagen matrix and myocardial stiffness in oim and wildtype littermates. A novel in vitro assay using neonatal cardiac myocytes cultured on elastic membranes patterned with collagen microchannels will be used to test the hypothesis that mechanical strain can regulate postnatal myofiber alignment. (2) DKO mice will be used to test the hypothesis that deletion of this small proteoglycan dysregulates post-infarction scar structure, mechanics and ventricular remodeling. Transmission electron microscopy shows abnormalities of microfibril organization in scar collagen of DKO mice. Therefore, mechanical properties will be measured in scars of DKO mice and wildtype littermates 2-8 weeks post-infarction. Microstructural models will be used to investigate the structural basis of altered scar mechanical properties. DKO and WT mice will be followed 4-6 months post-infarction to confirm the hypothesis that dysregulated scar structure accelerates the transition to congestive heart failure, as strongly suggested by preliminary observations. (3) Preliminary studies used novel techniques to micropattern aligned neonatal ventricular myocyte (NVM) cultures and subject them to anisotropic biaxial stretch. Micropatterned myocytes stretched transverse to the myofiber axis exhibited a significant hypertrophic response compared with those in which principal stretch was applied parallel to the myofibrils. By growing cells on different extracellular matrices, function-blocking antibodies and peptides will be used to determine whether these differential responses to anisotropic strain patterns are mediated via specific cell-matrix interactions while carefully controlling for cell shape, cell-cell contact and cell-matrix adhesion.